近似波線法による3次元不均質構造内での走時について

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書誌事項

タイトル別名
  • On the Travel Time Calculations by using Approximate Ray Tracing in a Laterally Heterogeneous Velocity Structure
  • キンジ ハセンホウ ニ ヨル 3ジゲン フキンシツ コウゾウナイ デ ノ ソウ

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抄録

Recently Approximate Ray Tracing Technique (ART) has been developed so that the travel time in a laterally heterogeneous media can be rapidly computed for a small region in which seismic ray paths are not too long (1 degree or less). In this paper, this technique is improved and applied to a slightly larger area of greater than 10 degree radial distance.<br>In addition more simple method (ART-0) with a increase in efficiency and small loss in accuracy was developed. In ART-0, the correction term of a heterogeneous media is calculated as the integral along the seismic ray path given by interpolation of Path Table (9 points for each path). This table is previously calculated in a lateraly homogenous standard model (Ichikawa and Mochizuki, 1971).<br>In a simple structure model of Japan which has only Pacific Plate, travel time residuals are about 5 or 10 times smaller than 1 dimensional structure model in case of ART-0 and ART, respectively. The computational time for ART is about 101 times larger than that for ART-0.<br>Hypocenter determination problem was also simulated by Monte-Carlo method in two cases; (1) shallow oceanside earthquake with poor azimuthal coverage of seismic stations, and (2) deep focus earthquake. Trial number of simulation is 50 for each case. 16 and 18 reading data of P wave are prepared by travel times of 3-dimensional ray tracing added by a normal random number with standard deviation of 0.05s and average of 0s. Although in both cases locations estimated by using 1 dimensional velocity structure model are systematically shifted by amount of 20 and 80km for case (1) and (2) respectively, the present method can determine the earthquke location accurately and rapidly. The accuracy of ART-0 was the same as that of ART, because the travel time difference between ART and ART-0 is nearly equal to errors of data.

収録刊行物

  • 地震　第２輯

    地震　第２輯 40 (1), 99-110, 1987

    公益社団法人 日本地震学会

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